Kosrae's Coast
Reducing coastal hazard risks on Kosrae
climate change
Future sea-level rise
In this section:
(C) Doug Ramsay & KIRMA, 2008
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Continued warming of the atmosphere and oceans will cause sea levels to continue to rise for many centuries to come, even if we manage to stabilise or reduce greenhouse gases.
By the end of this century:
- Sea levels will have risen by between 0.18 m to 0.59 m relative to sea levels over the period between 1980 and 1999 (light blue shaded areas in figure below).
- This assumes that contributions from Greenland and Antarctica ice caps remain at the same rate as measured between 1993 and 2003. If this rate increases in line with temperature increase there may be an additional 0.1 m to 0.2 m rise in sea level due to additional contribution from melting of the ice caps of Greenland and/or Antarctica (indicated by the dark blue shaded area in the figure below).
- Higher sea-level rises can not be ruled out as there is still a great deal of uncertainity associated with: 1) how Greenland and Antartica ice caps will respond to higher global temperatures, 2) regional variations in sea-level rise, and 3) certain climate processes that may influence sea-level rise rates. As such it is difficult to confidently estimate an upper bound for potential sea-level rise over this century and beyond.
The changes caused by climate change are gradual, occurring over many years. However, given the problems caused by erosion and coastal flooding at present, unless we start acting to reduce these risks now, the impacts caused by these hazards will become more severe. In terms of flooding of land, effects will include:
- Areas that are flooded at present, will be flooded more frequently in the future and flooding will be deeper.
- Present day "King Tide" levels (similar to the high tides that were experienced on Kosrae between November 2007 and February 2008) could be experienced by 31% to 100% of all high tides by the end of the century (see figure below).
- Areas that are just above present day flood levels will increasingly be flooded in the future.
- Increased drainage problems in low-lying land.
This figure shows how often high tides are exceeded on Kosrae.
The black line shows the present day. Very high 'King Tide' levels
(marked MHWPS) are exceeded by about 14% all high tides at present.
Under a sea-level rise of 0.18 m (green), present
day King tide levels will be exceed by about 32% of all high tides, by 91% if sea-level rise is 0.59 m (blue), and by every high tide
if sea-level rise is 0.79 m (red).
So by the end of this century, high tides such as those experienced over November 2007-February
2008 period will be experienced between 31% to 100% of the time.
Reducing greenhouse gas emissions is critical in limiting potentially catastrophic contributions to sea levels from the two major uncertainties associated with longer-term sea-level rise, that of the Greenland and West Antarctic Ice sheets. Catastrophic contributions to sea-level rise from collapse of the West Antarctic Ice Sheet or the rapid loss of the Greenland Ice Sheet are not considered likely to occur in the next fifty or so years, based on currently understanding. However, the occurrence of such catastrophic changes becomes increasingly more likely as greenhouse gas concentrations, and hence temperatures, continue to rise.
Global mean sea-level rise projections out to the 2090s (2090-2099).
The black line shows average global sea-levels from
1900 to 2005 as measured by tide gauges and satellites.
The red line is the annual average sea-level measured at Kwajalein
between 1947 and 2006.
The light blue shading shows the range in projected sea level out to the 2090s.
The dark blue shading
shows the potential additional contribution from Greenland and Antarctic Ice sheets if contributions to sea-level rise were to grow
linearly with global average temperature change.
Catastrophic sea-level rise
There is time to act to reduce many of the impacts that climate change will have on development around the coast of Kosrae. The
position of the coastline will change and this needs to be accepted and allowed. The important thing is to start to plan and implement
activities to ensure property and infrastructure such as roads are not seriously damaged. In many cases this will mean moving them
further landward away from the immediate coastline.
If we start by reducing the impacts caused by present day coastal hazards we will
significantly assist in reducing future impacts that may be exacerbated by climate change effects. The
Reduce Risk link above suggests
some ways that coastal hazard problems could be reduced on Kosrae.
Sea-level rise and other climate change effects will also cause the position of the coast to change. Effects will include:
- Retreat of the shoreline, loss of land and increased overwashing of the coastal margin. This is an important process as, although the coast retreats, overwashing allows the height of the land behind the beach to build up in response to sea-level rise. However, if seawalls have been built, this natural build up may not occur resulting in the long-term impacts being even greater..
- Possible changes to mangrove and swamp extent.